I like my friends brother. What do I do? How do I becomes friends with him without coming onto him too much?

My friends brother just came over from another country and has been here for about a week. I really like him already and he's really open and friendly. My friend would probably be like... "Um why do you like him?" We aren't supper close but we do talk often so she might find it odd that I would like him. Also we are both 16.